Abstract A33: Mediator is an intrinsically dynamic complex critical to Hsf1-activated transcription

Abstract

Abstract Mediator is an evolutionarily conserved transcriptional coactivator that plays a vital role in the regulation of RNA polymerase II (Pol II) transcribed genes in eukaryotes as diverse as yeast and human. It consists of a tri-modular core complex comprised of Head, Middle and Tail modules and a dissociable Cdk8/Kinase module (CKM). Although it has been assumed that core Mediator in the model eukaryote S. cerevisiae (budding yeast) exists as a stable 21-subunit complex based on cell-free assays, its structural state in vivo is unclear. We have obtained evidence that the Tail module is highly dynamic, and that a subcomplex consisting of Tail subunits Med2, Med3 and Med15 can be independently recruited to the UAS/promoter regions of Heat Shock Factor 1 (Hsf1)-regulated genes in response to acute thermal stress. Med2-Med3-Med15 autonomy is revealed by ChIP analysis following the “anchoring away” of select Mediator core subunits located in either Middle or Tail module. Such conditional depletion leads to a 60-80% reduction in HSP gene transcription. We additionally observed that Hsf1 can recruit the CKM independently of the core complex, and that both core Mediator and CKM recruitment occurs independently of SAGA. Collectively, our results indicate that yeast Mediator is intrinsically dynamic and that multiple species, including CKM-Mediator, the 21-subunit core complex, the Med2-Med3-Med15 Tail Triad and the four-subunit CKM, can be independently recruited by Hsf1 to its target genes. Citation Format: Jayamani Anandhakumar, Yara Moustafa, Surabhi Chowdhary, Amoldeep S. Kainth, David S. Gross. Mediator is an intrinsically dynamic complex critical to Hsf1-activated transcription. [abstract]. In: Proceedings of the AACR Special Conference on Chromatin and Epigenetics in Cancer; Sep 24-27, 2015; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2016;76(2 Suppl):Abstract nr A33.